JP6207732B2 - Method and system for controlling the shaft of a turbine generator with a static excitation system to reduce the amplitude of torsional vibrations due to industrial load fluctuations - Google Patents

Description

  The present invention relates to the field of power generation facilities, and more particularly to torsional vibration of power generation facilities.

  The turbine generator includes a rotating shaft for converting mechanical motion into electric power. In this case, torsional vibrations can be induced in the shaft by the fluctuating load coupled with the generator. Due to fluctuating loads (such as electric arc furnaces), the generator power can cause rapid transients, which can cause various levels of rotation on the generator's rotating shaft. Torsional vibration may be induced. Depending on the timing at which such a transient state occurs, there is a possibility that even though the vibration is originally small, the small vibration is strengthened and a torsional vibration having a considerably large amplitude is formed. Various approaches have been tried to attenuate such torsional vibration. What has been done so far in these approaches is the filtering and leveling of the load fed by the generator, thereby reducing the amplitude when the load is in some transient state, as well as such transients. It was going to reduce the repeatability of the state.

  One aspect of the invention relates to a system for controlling a shaft of a turbine generator with a static excitation system, where the shaft is driven in a first rotational direction at a predetermined speed. . The system includes a detector, which is configured to receive a velocity signal from a velocity sensor and detect a torsional vibration signal corresponding to the torsional vibration of the shaft based on the velocity signal. The system further includes an amplifier having a controllable gain and an automatic voltage regulator. In this case, the amplifier is configured to generate a control signal based on the torsional vibration signal, and the automatic voltage regulator receives the control signal and based on the control signal, from the turbine generator by the static excitation system. It is configured to control the amount of power extracted.

  Another aspect of the present invention relates to a method for controlling a shaft of a turbine generator with a static excitation system, wherein the shaft is driven in a first rotational direction at a predetermined speed. . In this method, a step of detecting torsional vibration of a shaft, a step of calculating a control signal based on the torsional vibration, and an amount of electric power extracted from a turbine generator by a static excitation system are controlled using this control signal. And steps to include.

  The following claims are set forth at the end of this specification, which clearly represents the invention and which clearly claims the scope of its rights, but with reference to the accompanying drawings: The explanation will deepen the understanding of the present invention. In the drawings, similar members are denoted by the same reference numerals.

Diagram showing an example of a static excitation system for a turbine generator according to the prior art Figure showing a turbine generator constructed according to the basic principle of the present invention Block diagram conceptually showing how an auxiliary control signal can be injected into a static excitation system in accordance with the basic principles of the present invention. The figure which shows an example of the signal waveform of the static type excitation control system by the basic principle of this invention The figure which shows an example of the signal waveform of the static type excitation control system by the basic principle of this invention A flow chart illustrating an example of a method for controlling a static excitation system according to the basic principles of the present invention.

  In the following detailed description of the advantageous embodiments, reference is made to the accompanying drawings that form a part hereof, and in which is shown by way of illustration and not limitation, specific embodiments in which the invention may be practiced. An advantageous embodiment is shown. It is obvious that other embodiments may be adopted and changes may be made without departing from the concept and scope of the present invention.

  In a generator that uses a field coil rather than a permanent magnet, current must flow through the field coil to make the device operable. If the field coil is not fed, it cannot rotate at all if it is a rotor of an electric motor, whereas it can rotate if it is a rotor of a generator, but no effective electrical energy is generated at that time. FIG. 1A shows an example of a static excitation system according to the prior art. In this case, the generator includes a generator rotating field 102 and a stationary generator stator 104. As is well known, the generators are connected by a three-wire bus 106 to supply the generated power to the power transmission network 101.

  The voltage and current of the power generated by the generator can be sampled or sensed so that the current operating status of the generator can be represented. The generated voltage and current are not readily available even by conventional automatic voltage regulator (AVR) circuit 112, and thus a current and voltage transformer 108 is utilized to provide a signal from bus 106. Can be reduced to an easily usable signal by the automatic voltage regulator 112.

  A static exciter 116 is also connected to the three-wire bus 106 via a transformer 110, whereby electric power can be supplied to the exciter 116. In the case of the circuit shown as an example in FIG. 1A, the exciter 116 includes a thyristor bridge with six thyristors 118, which are connected to the exciter transformer 110 and the generator field 102. The automatic voltage regulator 112 supplies a DC control signal 120 that drives the thyristor 118. Based on the value of the control signal 120, the exciter output voltage 122 is supplied to the generator field 102.

  As is well known, the voltage regulator 112 is designed to generate the control signal 120 such that the operating characteristics of the generator can be changed to more closely reproduce the ideal operating parameters. As will be appreciated by those skilled in the art, the circuit of FIG. 1A is only an example to illustrate the basic principles of a static exciter or “static excitation system” (used herein) for a turbine generator. Rather, the same result can be achieved with other functionally equivalent circuits.

  An aspect of the present invention relates to a method and apparatus for performing auxiliary control of a static excitation system in a turbine generator. This auxiliary control is used to adjust the exciter output voltage to stabilize the torsional vibration induced in the rotor due to fluctuations in the industrial load, and to A feedback signal from the measurement can be used.

  This feedback signal may be generated from one or more speed sensors that measure the instantaneous speed of the turbine generator rotor. In order to generate an auxiliary control signal, this feedback signal can be detected to generate a torsional velocity or displacement signal that can be processed and sent out by a suitable filter, phase shift function and amplification. This auxiliary control signal can then be injected into the voltage regulator of the static excitation system to control the instantaneous power of the generator field.

  FIG. 1B shows a turbine generator constructed in accordance with the basic principles of the present invention. The turbine generator includes a rotating shaft for converting mechanical motion into electric power. In this case, a torsional vibration may be induced on the shaft by the variable load 162 coupled to the generator. According to the basic principle of the invention, this type of torsional vibration can be detected by measuring the speed at which the shaft rotates.

  Referring to FIG. 1B, the static excitation system 154 can extract power 152 from the generator 150. The amount of power 152 extracted can be automatically controlled by voltage regulator 156. The voltage regulator 156 can receive inputs from a transformer (VT) 146 and a current transformer (CT) 148 so that the voltage control signal for the static excitation system 154 can be used for current operation of the generator 150. Determined based on the situation.

  As described above, the speed sensor 158 can be used to measure the rotational speed of the rotating shaft of the generator 150. For example, a toothed wheel or a notched wheel can be coupled to the axis of rotation so that when the axis rotates, the wheel rotates as well. In this case, the wheel may be coupled directly to the rotating shaft, or the wheel may be indirectly coupled to the rotating shaft via various gears or link mechanisms. One or more speed sensors that detect the passage of wheel teeth or notches may be added to the wheel. Such detection can be accomplished, for example, using an optical sensor that recognizes a visual difference between a notch or tooth and other parts of the wheel. As will be apparent to those skilled in the art, a number of alternative techniques can be used to measure the rotational speed of the shaft without departing from the scope of the present invention.

  The speed sensor signal generated by the sensor 158 can be detected by the torsion detector 160 and the torsion speed signal 161 can be extracted. Since the shaft is driven in a known direction at a known speed (eg 3600 RPM or 1800 RPM), a known ideal speed value will be generated by the detected notch or tooth if no torsional vibration has occurred. Become. However, if a torsional vibration occurs and it is in the direction opposite to the driving direction, the measured shaft speed is less than the expected ideal value. Similarly, if the torsional vibration is in the same direction as the drive direction, the measured axial speed will be greater than the expected ideal value. Therefore, the torsional speed signal 161 can be calculated based on the speed signal measured by the speed sensor 158, which indicates how far the shaft speed deviates from the expected speed value, and the vibration frequency. Is also represented. This torsional speed signal 161 can then be used to generate an auxiliary control signal 165 for the static excitation system 154 of the generator 150. Specifically, the static excitation system 154 can be controlled to stabilize system operation by canceling torsional vibrations.

  As shown in FIG. 1B, the torsional velocity signal 161 can be sent through a bandpass filter 164 to pass only the desired frequency band. For example, in the case of a 2-pole 60 Hz generator, a subharmonic signal (for example, 5 Hz to 20 Hz) can be in an appropriate frequency range. In the case of a 4-pole power generation system, the same frequency as described above may be used, or the frequency of another subharmonic signal may be targeted. Undesirable noise and other non-twisted components can be filtered or blocked by the bandpass filter 164. Filtered signal 163 can then be passed through phase compensation circuitry and amplifier 166 to generate auxiliary control signal 165. The gain of the amplifier 166 is designed such that a control signal 165 of the proper amplitude is generated from a predetermined amplitude speed change (ie, the torsional speed signal 161) to provide the desired effect on the static excitation system 154. . The phase compensation network 166 is designed so that the phase of the output control signal 165 matches the phase of the input filtering signal 163. As will be apparent to those skilled in the art, a variety of different amplifiers and compensation circuits, software, or digital signal processors may be implemented to achieve the above results without departing from the scope of the present invention. .

  Thereafter, the auxiliary control signal 165 is introduced into the static excitation system 154 by adding the auxiliary control signal 165 to the normal control signal already used for output voltage control of the static exciter. Can do.

  FIG. 1C shows a block diagram conceptually illustrating how an auxiliary control signal can be injected into a static excitation system in accordance with the basic principles of the present invention. The elements within the dashed block 168 shown in FIG. 1B are grouped together as a single block element 168 in FIG. 1C. Block 168 generates an auxiliary control signal 165 that can be combined by adder 184 with control signal 181 from voltage regulator 156. The behavior of the static excitation system 154 can be controlled to generate the field voltage 188 applied to the generator field 190 using the control signal 186 synthesized in this way.

  As will be apparent to those skilled in the art, many different approaches are possible for synthesizing signals 165 and 181 without departing from the scope of the present invention. Specifically, the control signal should be placed in a standard generator voltage control loop so that the control signal does not adversely affect the voltage control of the generator or the generator terminal voltage or reactive power is not biased. Can be injected into.

  During operation, the increase and decrease in field voltage output by the static excitation system 154 is proportional to the increase or decrease in the amount of power in the static excitation system that is removed from the generator. In a steady state, the static excitation system generates a predetermined operating voltage and extracts a predetermined amount of power from the generator. Thus, when the voltage supplied by the static excitation system increases or decreases from its steady state operating voltage, the power drawn from the generator is increased or decreased, respectively. When the electric power extracted from the generator is increased by the static excitation system, a drag action that resists the rotation of the shaft in the shaft driving direction acts on the rotating generator shaft. As the power drawn by the static excitation system is reduced, the drag action is reduced, resulting in an increase in shaft rotational speed in the axial drive direction.

  2A and 2B show examples of signal waveforms of the static excitation control system according to the basic principle of the present invention. In FIG. 2A, the vertical axis 202 represents the difference between the measured axial speed of the rotating generator and the expected axial speed. The horizontal axis 204 represents time, indicating that the signal 163 has a period “t” 206. The signal 163 (see FIG. 1B) can be a signal filtered by the bandpass filter 164. The signal 163 has a positive amplitude value portion 212 that indicates that the generator shaft is oscillating in the same rotational direction as the axial drive direction. In contrast, what is represented by signal 163 in region 214 is that the shaft is oscillating in a direction of rotation opposite to the axial drive direction. Regions 212 and 214 are connected by a zero cross point 216. The frequency and amplitude of these vibrations are acquired by parameters “amplitude” 210 and “period t” 206.

  The phase compensation and gain circuit 166 can receive the signal 163 and generate an appropriate output signal 165 as shown in FIG. 2B. As described above, when the signal 163 is in the region 212, the generator shaft can be dragged by increasing the power drawn by the static excitation system 154. This increase is represented by the first portion 222 of the control signal 165. If the shaft is rotating slower than expected (eg, portion 214), the power drawn by the static excitation system voltage can be reduced to effectively increase the rotational speed of the shaft.

  The amplitude 230 of the control signal 165 may be derived empirically through experimentation and / or for any particular static excitation circuit implemented, the level of the control signal 165 and the shaft rotation of the generator It may be derived through tests to determine the correlation between the resulting effect on speed. Accordingly, the gain of the amplifier can be set so that a control signal 165 that has the desired effect on the rotating shaft can be generated. The timing of the control signal 165 is based on a vibration frequency that can be calculated from the zero cross point 216 shown in FIG. 2A. For example, in the case of rotational vibration of 10 Hz, the signal 163 in FIG. 2A has a period of 0.1 second. During one half of this period (ie 0.05 seconds), the shaft rotates faster than expected, ie, the control signal 165 now has a positive amplitude. During the other half of this period, the axis rotates slower than expected and the control signal 165 has a negative amplitude. The phase compensation circuit 166 ensures that the voltage of the stationary excitation system 154 is generated based on the phase of the control signal 165 so as to cancel the generated rotational vibration.

  As will be apparent to those skilled in the art, feedback and control systems can be designed in various ways without departing from the scope of the present invention. For example, the polarity of the control signal may be reversed from the previously described polarity, in which case the circuit is also designed to cause the shaft to rotate in the desired direction (ie, the direction opposite to torsional vibration). .

  In this way, stabilization of torsional vibrations can be achieved by a technique that takes advantage of the components of the static excitation system already provided in existing power equipment. If there are additional components, they are low-power devices that detect and process. The power facility operator can then perform torsional vibration control internally within the power plant without having to rely on the industrial load customer to change the customer's process or facility.

  FIG. 3 shows a flowchart illustrating an example of a method for controlling a static excitation system according to the basic principle of the present invention. In step 302, the instantaneous rotational speed of the generator shaft is detected. As described above, various methods and sensors can be used to determine how fast the shaft is rotating. The rate at which the shaft speed is sampled depends on the frequency range of torsional vibrations that are likely to occur. An example of this range is torsional vibration in the range of about 5-20 Hz. In the case of torsional vibration within this frequency range, the speed may be read out every millisecond.

  In step 304, the axial velocity is detected to form a torsional vibration signal in which the amplitude and torsional vibration frequency can be detected. In this case, the shaft of the generator is driven in the first rotation direction at a speed determined in advance. Therefore, the difference between the measured shaft speed and the speed obtained in advance indicates how much the shaft is torsionally vibrated. In the first part of the vibration, the shaft twists in the same direction as the driving direction of the shaft, and in the second part of the vibration, the shaft twists in the direction opposite to the driven state. The amplitude of the torsional vibration is represented by the magnitude of the difference between the measured shaft speed and the previously determined shaft speed. The frequency of torsional vibration is represented by how fast the direction of vibration changes. Thus, in step 304, these two values (ie, amplitude and frequency) can be determined. According to at least one embodiment, the torsional vibration amplitude and frequency need not be explicitly calculated. In that case, the control signal may be based on the deviation of the instantaneous speed from the ideal shaft rotation speed. In this embodiment, the instantaneous velocity deviation value (ie, signal 161 in FIG. 1B) is sampled and can then be bandpass filtered (or phase shifted and filtered). The filtered signal samples can then be amplified by an appropriate amount to generate a control signal (ie, signal 165 in FIG. 1B) that is fed back to the voltage regulator (ie, 156 in FIG. 1B). The In other words, an explicit amplification of the torsional speed is not calculated, and no matter what the value of the filtered signal value is, it is amplified with a predetermined gain. In this way, based on the detected instantaneous speed deviation, the control signal is applied with proper characteristics, proper polarity, proper amplitude, and proper frequency.

  In step 306, the amplitude of the control signal is determined based on the amplitude of the torsional vibration. For example, the control signal may be based on instantaneous velocity deviations or based on the maximum amplitude measured during one half cycle of one torsional vibration. As described above, the amplifier (or similar circuit) is configured to have a gain that generates a control signal that causes the generator shaft to rotate in the proper direction and at the desired speed. In step 308, the control signal is applied over an appropriate length of time using the frequency of the torsional vibration. As already mentioned, if one period of torsional vibration is 0.1 second, the control signal is transmitted over one half period of the period with one polarity and then over the other half period of the period with the opposite polarity. Can be applied. If the shaft is rotated faster than the speed at which the shaft is driven due to torsional vibrations, the control signal increases the power that the static excitation system draws from the generator. As a result, the shaft is actually rotated in the opposite direction to the state in which the shaft is driven (that is, the shaft is decelerated). If the shaft is rotated slower than the speed at which the shaft is driven due to torsional vibrations, the control signal reduces the power that the static excitation system draws from the generator. This actually causes the shaft to rotate in the same direction as the shaft is driven (ie, the shaft accelerates).

  While specific embodiments of the present invention have been illustrated and described above, it will be apparent to those skilled in the art that various changes and modifications can be made without departing from the spirit and scope of the present invention. it can. Accordingly, the appended claims are intended to cover all such changes and modifications that are within the scope of this invention.

Claims (8)

A method for controlling a shaft of a turbine generator with a static excitation system comprising:
The shaft is driven in a first rotational direction at a predetermined speed, the method comprising:
Detecting torsional vibrations of the shaft;
Calculating a control signal based on the torsional vibration;
Using the control signal to control the amount of power drawn from the turbine generator by the static excitation system ;
Measuring the rotational speed of the shaft,
The torsional vibration includes a first amplitude corresponding to a difference between the measured rotational speed and the predetermined speed;
The torsional vibration includes a first portion and a second portion;
The first portion lasts for a first period of time and corresponds to the first direction of rotation;
The second portion lasts for a second period of time and corresponds to a second direction of rotation opposite to the first direction of rotation;
The torsional vibration has a frequency corresponding to a reciprocal of a sum of the first period and the second period;
Determining a second amplitude of the control signal based on the first amplitude;
Applying the control signal to the stationary excitation system according to the second amplitude and a first polarity during the first period;
Applying the control signal to the stationary excitation system with the second amplitude and a second polarity during the second period that is opposite in polarity to the first polarity;
including,
It is characterized by
A method for controlling a shaft of a turbine generator with a static excitation system. The static excitation system increases the amount of power drawn from the turbine generator during the first period by the control signal;
The method of claim 1 . The static excitation system reduces the amount of power drawn from the turbine generator during the second period by the control signal;
The method of claim 1 . It said control signal, further comprising the step of injecting the automatic voltage regulator of the static excitation system,
The method of claim 1. A system for controlling a shaft of a turbine generator equipped with a static excitation system,
The shaft is driven in a first rotational direction at a predetermined speed, and the system is
A detector configured to receive a speed signal from a speed sensor and to detect a torsional vibration signal corresponding to the torsional vibration of the shaft based on the speed signal;
A signal generator having a controllable gain and configured to generate a control signal based on the torsional vibration signal;
Receiving said control signal, based on the control signal, look including an automatic voltage regulator configured to control the amount of power taken from the turbine generator by the static excitation system,
The speed sensor is configured to measure the rotational speed of the shaft;
The torsional vibration signal includes a first amplitude corresponding to a difference between the measured rotational speed and the predetermined speed;
The torsional vibration signal includes a first portion and a second portion;
The first portion lasts for a first period of time and corresponds to the first direction of rotation;
The second portion lasts for a second period of time and corresponds to a second direction of rotation opposite to the first direction of rotation;
The torsional vibration signal has a frequency corresponding to a reciprocal of a sum of the first period and the second period;
An amplifier gain is adjusted based on the first amplitude to generate a second amplitude of the control signal;
The control signal is supplied to the automatic voltage regulator by the second amplitude and the first polarity during the first period;
The control signal is supplied to the automatic voltage regulator by the second amplitude and a second polarity during the second period that is opposite in polarity to the first polarity.
A system that controls the shaft of a turbine generator equipped with a static excitation system. The static excitation system increases the amount of power drawn from the turbine generator during the first period by the control signal;
The system of claim 5 . The static excitation system reduces the amount of power drawn from the turbine generator during the second period by the control signal;
The system of claim 5 . Said control signal, and configured synthesizer is further provided to combine the separately formed other voltage control signal,
The system of claim 5 .

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